Thermoacoustic device array

ABSTRACT

A thermoacoustic device array includes a substrate and a plurality of thermoacoustic device units located on a surface of the substrate. The substrate defines a number of recesses on the surface, and the recesses are spaced from and parallel with each other. Each thermoacoustic device unit includes a sound wave generator, a first electrode and a second electrode. The first electrode and the second electrode are spaced from each other and electrically connected to the sound wave generator. The sound wave generator is located on the surface and suspended over the recesses. At least one of the recesses is located between the first electrode and the second electrode, and one portion of the sound wave generator that is between the first electrode and the second electrode is suspended over the at least one of the recesses.

RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201210471286.2, filed on Nov. 20, 2012 inthe China Intellectual Property Office, the contents of which are herebyincorporated by reference. This application is related tocommonly-assigned applications entitled, “METHOD FOR MAKINGTHERMOACOUSTIC DEVICE ARRAY”, filed on Jun. 28, 2013, with applicationSer. No. 13/931508, the contents of the above commonly-assignedapplications are hereby incorporated by reference.

BACKGROUND

1. Technical Field

The present disclosure relates to thermoacoustic device arrays andmethod for making the same.

2. Description of Related Art

An acoustic device generally includes an electrical signal output deviceand a loudspeaker. The electrical signal output device inputs electricalsignals into the loudspeaker. The loudspeaker receives the electricalsignals and then transforms them into sounds.

There are different types of loudspeakers that can be categorizedaccording by their working principles, such as electro-dynamicloudspeakers, electromagnetic loudspeakers, electrostatic loudspeakersand piezoelectric loudspeakers.

Thermoacoustic effect is a conversion of heat to acoustic signals. Thethermoacoustic effect is distinct from the mechanism of the conventionalloudspeaker, which the pressure waves are created by the mechanicalmovement of the diaphragm. When signals are inputted into a sound wavegenerator, heating is produced in the sound wave generator according tothe variations of the signal and/or signal strength. Heat is propagatedinto surrounding medium. The heating of the medium causes thermalexpansion and produces pressure waves in the surrounding medium,resulting in sound wave generation. Such an acoustic effect induced bytemperature waves is commonly called “the thermoacoustic effect”.

Carbon nanotubes (CNT) are a novel carbonaceous material havingextremely small size and extremely large specific surface area. Carbonnanotubes have received a great deal of interest since the early 1990s,and have interesting and potentially useful electrical and mechanicalproperties, and have been widely used in a plurality of fields. Thecarbon nanotube film used in the thermoacoustic device has a largespecific surface area, and extremely small heat capacity per unit areathat make the sound wave generator emit sound audible to humans.However, the carbon nanotube film used in the thermoacoustic device hasa small thickness and a large area, and is likely to be damaged by theexternal forces applied thereon.

What is needed, therefore, is to provide a thermoacoustic device forsolving the problem discussed above.

BRIEF DESCRIPTION OF THE DRAWINGS

Many aspects of the embodiments can be better understood with referencesto the following drawings. The components in the drawings are notnecessarily drawn to scale, the emphasis instead being placed uponclearly illustrating the principles of the embodiments. Moreover, in thedrawings, like reference numerals designate corresponding partsthroughout the several views.

FIG. 1 is a schematic view of one embodiment of a thermoacoustic devicearray.

FIG. 2 is an exploded, isometric view of a thermoacoustic device unit ofthe thermoacoustic device array of FIG. 1.

FIG. 3 is a transverse, cross-sectional view of the thermoacousticdevice unit of FIG. 2 along line III-III.

FIG. 4 is a photograph of the thermoacoustic device array of FIG. 1.

FIG. 5 shows a scanning electron microscope (SEM) image of a carbonnanotube film in the thermoacoustic device unit.

FIG. 6 shows an SEM image of an untwisted carbon nanotube wire.

FIG. 7 shows an SEM image of a twisted carbon nanotube wire.

FIG. 8 is a flowchart of one embodiment of a method for making thethermoacoustic device array of FIG. 1.

FIG. 9 shows a photomicrograph of a carbon nanotube wire soaked by anorganic solution.

FIG. 10 is a schematic view of another embodiment of a thermoacousticdevice array.

FIG. 11 is an exploded, isometric view of a thermoacoustic device unitof the thermoacoustic device array of FIG. 10.

FIG. 12 is a transverse, cross-sectional view of the thermoacousticdevice unit of FIG. 11.

FIG. 13 is an exploded, isometric view of another embodiment of athermoacoustic device unit of the thermoacoustic device array.

FIG. 14 is a transverse, cross-sectional view of another embodiment of athermoacoustic device unit of the thermoacoustic device array.

FIG. 15 is a flowchart of one embodiment of a method for forming aplurality of cutting lines.

FIG. 16 is a flowchart of one embodiment of a method for forming aplurality of recesses.

FIG. 17 is a flowchart of one embodiment of a method for forming a soundwave generator on a substrate.

DETAILED DESCRIPTION

The disclosure is illustrated by way of example and not by way oflimitation in the figures of the accompanying drawings in which likereferences indicate similar elements. It should be noted that referencesto “an” or “one” embodiment in this disclosure are not necessarily tothe same embodiment, and such references mean at least one.

Referring to FIGS. 1-4, a thermoacoustic device array 10 includes asubstrate 100 and a plurality of thermoacoustic device units 200. Thesubstrate 100 includes a first surface 101. The plurality ofthermoacoustic device units 200 is located on the first surface 101 ofthe substrate 100. Each of the plurality of thermoacoustic device units200 includes a sound wave generator 110, a first electrode 130, and asecond electrode 140. A plurality of recesses 102 is defined by thesubstrate 100. The plurality of recesses 102 are spaced from each otherand located on the first surface 101 of the substrate 100. The soundwave generator 110 is attached on the first surface 101 and is suspendedover the plurality of recesses 102. The first electrode 130 and thesecond electrode 140 are spaced from each other. At least one recess 102is located between the first electrode 130 and the second electrode 140.The first electrode 130 and the second electrode 140 are electricallyconnected to the sound wave generator 110.

The substrate 100 is a flake-like structure. The shape of the substrate100 can be circular, square, rectangular or other geometric figure. Theresistance of the substrate 100 is greater than the resistance of thesound wave generator 110 to avoid a short through the substrate 100. Thesubstrate 100 can have a good thermal insulating property, therebypreventing the substrate 100 from absorbing the heat generated by thesound wave generator 110. The material of the substrate 100 can besingle crystal silicon or multicrystalline silicon. The size of thesubstrate 100 ranges from about 25 square millimeters to about 100square millimeters. In one embodiment, the substrate 100 is singlecrystal silicon with a thickness of about 0.6 millimeters, and a lengthof each side of the substrate 100 is about 10 centimeters.

The plurality of thermoacoustic device units 200 is independent fromeach other. The term “independent from each other” means that the soundwave generators 110 of adjacent two thermoacoustic device units 200 areinsulated from each other and work individually by the inputtingdifferent signals. Adjacent two thermoacoustic device units 200 arelocated independently by a plurality of cutting lines 105. The pluralityof cutting lines 105 is located on the first surface 101 and defined bythe substrate 100. The location of the plurality of cutting lines 105 isselected according to number of the thermoacoustic device units 200 andarea of the substrate. In one embodiment, the plurality of cutting lines105 are substantially parallel with or perpendicular to each other. Theshape of the cutting line 105 can be a through hole, a blind recess(i.e., a depth of the cutting line 105 is less than a thickness of thesubstrate 100), a blind hole.

The plurality of the thermoacoustic device units 200 is dispersed on thesurface 101 of the substrate 100 and arranged to form an array. Thenumber of the thermoacoustic device units 200 is selected according toneed. In one embodiment, the number of the thermoacoustic device units200 is eight.

The plurality of recesses 102 can be uniformly dispersed on the firstsurface 101 such as dispersed in an array. The plurality of recesses 102can also be randomly dispersed. In one embodiment, the plurality ofrecesses 102 extends along the same direction, and spaced from eachother with a certain distance. The shape of the recess 102 can be athrough hole, a blind recess (i.e., a depth of the recess 102 is lessthan a thickness of the substrate 100), or a blind hole. Each of theplurality of recesses 102 includes a bottom and a sidewall adjacent tothe bottom. The first portion 112 is spaced from the bottom and thesidewall. A bulge 104 is formed between the adjacent two recesses 102.

A depth of the recess 102 can range from about 100 micrometers to about200 micrometers. The sound waves reflected by the bottom surface of theblind recesses may have a superposition with the original sound waves,which may lead to an interference cancellation. To reduce this impact,the depth of the blind recesses that can be less than about 200micrometers. In another aspect, when the depth of the blind recesses isless than 100 micrometers, the heat generated by the sound wavegenerator 110 would be dissipated insufficiently. To reduce this impact,the depth of the blind recesses and holes can be greater than 100micrometers.

The plurality of recesses 102 can parallel with each other and extendalong the same direction. A distance d₁ between adjacent two recesses102 can range from about 20 micrometers to about 200 micrometers. Thusthe first electrode 130 and the second electrode 140 can be printed onthe substrate 100 via nano-imprinting method. A cross section of therecess 102 along the extending direction can be V-shaped, rectangular,or trapezoid. In one embodiment, a width of the recess 102 can rangefrom about 0.2 millimeters to about 1 micrometer. Thus, sound wavegenerator 110 can be prevented from being broken. Furthermore, a drivenvoltage of the sound wave generator 110 can be reduced to lower than12V. In one embodiment, the driven voltage of the sound wave generator110 is lower than or equal to 5V. In one embodiment, the shape of therecess 102 is trapezoid. An angle α is defined between the sidewall andthe bottom. The angle α is equal to the crystal plane angle of thesubstrate 100. In one embodiment, the width of the recess 102 is about0.6 millimeters, the depth of the recess 102 is about 150 micrometers,the distance d₁ between adjacent two recesses 102 is about 100micrometers, and the angle α is about 54.7 degrees.

The thermoacoustic device array 10 further includes an insulating layer120. The insulating layer 120 can be a single-layer structure or amulti-layer structure. In one embodiment, the insulating layer 120 canbe merely located on the plurality of bulges 104. In another embodiment,the insulating layer 120 is a continuous structure, and attached on theentire first surface 101. The insulating layer 120 covers the pluralityof recesses 102 and the plurality of bulges 104. The sound wavegenerator 110 is insulated from the substrate 100 by the insulatinglayer 120. In one embodiment, the insulating layer 120 is a single-layerstructure and covers the entire first surface 101.

The material of the insulating layer 120 can be SiO₂, Si₃N₄, orcombination of them. The material of the insulating layer 120 can alsobe other insulating materials. A thickness of the insulating layer 120can range from about 10 nanometers to about 2 micrometers, such as 50nanometers, 90 nanometers, and 1 micrometer. In one embodiment, thethickness of the insulating layer is about 1.2 micrometers.

The sound wave generator 110 is located on the first surface 101 andinsulated from the substrate 100 by the insulating layer 120. The soundwave generator 110 defines a first portion 112 and a second portion 114.The first portion 112 is suspended over the plurality of recesses 102,and the second portion 114 is attached on the plurality of bulges 104.The second portion 114 can be attached on the plurality of bulges 104via an adhesive layer or adhesive particles (not shown).

The sound wave generator 110 has a very small heat capacity per unitarea. The heat capacity per unit area of the sound wave generator 110 isless than 2×10⁻⁴ J/cm²*K. The sound wave generator 110 can be aconductive structure with a small heat capacity per unit area and asmall thickness. The sound wave generator 110 can have a large specificsurface area for causing the pressure oscillation in the surroundingmedium by the temperature waves generated by the sound wave generator110. The sound wave generator 110 can be a free-standing structure. Theterm “free-standing” includes, but is not limited to, a structure thatdoes not have to be supported by a substrate and can sustain the weightof it when it is hoisted by a portion thereof without any significantdamage to its structural integrity. The suspended part of the sound wavegenerator 110 will have more sufficient contact with the surroundingmedium (e.g., air) to have heat exchange with the surrounding mediumfrom both sides of the sound wave generator 110. The sound wavegenerator 110 is a thermoacoustic film.

The sound wave generator 110 can be or include a free-standing carbonnanotube structure. The carbon nanotube structure may have a filmstructure. The thickness of the carbon nanotube structure may range fromabout 0.5 nanometers to about 1 millimeter. The carbon nanotubes in thecarbon nanotube structure are combined by van der Waals attractive forcetherebetween. The carbon nanotube structure has a large specific surfacearea (e.g., above 30 m²/g). The larger the specific surface area of thecarbon nanotube structure, the smaller the heat capacity per unit areawill be. The smaller the heat capacity per unit area, the higher thesound pressure level of the sound produced by the sound wave generator110.

The carbon nanotube structure can include at least one carbon nanotubefilm, a plurality of carbon nanotube wires, or a combination of carbonnanotube film and the plurality of carbon nanotube wires.

The carbon nanotube film can be a drawn carbon nanotube film formed bydrawing a film from a carbon nanotube array that is capable of having afilm drawn therefrom. The heat capacity per unit area of the drawncarbon nanotube film can be less than or equal to about 1.7×10⁻⁶J/cm²*K. The drawn carbon nanotube film can have a large specificsurface area (e.g., above 100 m²/g). In one embodiment, the drawn carbonnanotube film has a specific surface area in the range from about 200m²/g to about 2600 m²/g. In one embodiment, the drawn carbon nanotubefilm has a specific weight of about 0.05 g/m².

The thickness of the drawn carbon nanotube film can be in a range fromabout 0.5 nanometers to about 100 nanometers. When the thickness of thedrawn carbon nanotube film is small enough (e.g., smaller than 10micrometeras), the drawn carbon nanotube film is substantiallytransparent.

Referring to FIG. 5, the drawn carbon nanotube film includes a pluralityof successive and oriented carbon nanotubes joined end-to-end by van derWaals attractive force therebetween. The carbon nanotubes in the drawncarbon nanotube film can be substantially oriented along a singledirection and substantially parallel to the surface of the carbonnanotube film. Furthermore, an angle β can exist between the orienteddirection of the carbon nanotubes in the drawn carbon nanotube film andthe extending direction of the plurality of recesses 102, and 0<β≦90°.In one embodiment, the oriented direction of the plurality of carbonnanotubes is perpendicular to the extending direction of the pluralityof recesses 102. As can be seen in FIG. 5, some variations can occur inthe drawn carbon nanotube film. The drawn carbon nanotube film is afree-standing film. The drawn carbon nanotube film can be formed bydrawing a film from a carbon nanotube array that is capable of having acarbon nanotube film drawn therefrom. Furthermore, the plurality ofcarbon nanotubes are substantially parallel with the first surface 101.

The carbon nanotube structure can include more than one carbon nanotubefilms. The carbon nanotube films in the carbon nanotube structure can becoplanar and/or stacked. Coplanar carbon nanotube films can also bestacked one upon other coplanar films. Additionally, an angle can existbetween the orientation of carbon nanotubes in adjacent films, stackedand/or coplanar. Adjacent carbon nanotube films can be combined by onlythe van der Waals attractive force therebetween without the need of anadditional adhesive. The number of the layers of the carbon nanotubefilms is not limited. However, as the stacked number of the carbonnanotube films increases, the specific surface area of the carbonnanotube structure will decrease. A large enough specific surface area(e.g., above 30 m²/g) must be maintained to achieve an acceptableacoustic volume. An angle θ between the aligned directions of the carbonnanotubes in the adjacent two drawn carbon nanotube films can range fromabout 0 degrees to about 90 degrees. Spaces are defined between adjacenttwo carbon nanotubes in the drawn carbon nanotube film. When the angle θbetween the aligned directions of the carbon nanotubes in adjacent drawncarbon nanotube films is larger than 0 degrees, a microporous structureis defined by the carbon nanotubes in the sound wave generator 110. Thecarbon nanotube structure in an embodiment employing these films willhave a plurality of micropores. Stacking the carbon nanotube films willadd to the structural integrity of the carbon nanotube structure.

The plurality of carbon nanotube wires are parallel with and spaced fromeach other. The plurality of carbon nanotube wires are intersected withthe plurality of recesses 102. In one embodiment, the plurality ofcarbon nanotube wires is perpendicular to the plurality of recesses 102.Each of the plurality of carbon nanotube wires includes a plurality ofcarbon nanotubes, and the extending direction of the plurality of carbonnanotubes is parallel with the carbon nanotube wire. The plurality ofcarbon nanotube wires is suspended over the plurality of recesses 102.

A distance between adjacent two carbon nanotube wires ranges from about1 micrometers to about 200 micrometers, such as 50 micrometers, 150micrometers. In one embodiment, the distance between adjacent tow carbonnanotube wires is about 120 micrometers. A diameter of the carbonnanotube wire ranges from about 0.5 nanometers to about 100 micrometers.In one embodiment, the distance between adjacent two carbon nanotubewires is about 120 micrometers, and the diameter of the carbon nanotubewire is about 1 micrometer.

The carbon nanotube wire can be untwisted or twisted. Treating the drawncarbon nanotube film with a volatile organic solvent can form theuntwisted carbon nanotube wire. Specifically, the organic solvent isapplied to soak the entire surface of the drawn carbon nanotube film.During the soaking, adjacent parallel carbon nanotubes in the drawncarbon nanotube film will bundle together, due to the surface tension ofthe organic solvent as it volatilizes, and thus, the drawn carbonnanotube film will be shrunk into untwisted carbon nanotube wire.Referring to FIG. 6, the untwisted carbon nanotube wire includes aplurality of carbon nanotubes substantially oriented along a samedirection (i.e., a direction along the length of the untwisted carbonnanotube wire). The carbon nanotubes are parallel to the axis of theuntwisted carbon nanotube wire. More specifically, the untwisted carbonnanotube wire includes a plurality of successive carbon nanotubesegments joined end to end by van der Waals attractive forcetherebetween. Each carbon nanotube segment includes a plurality ofcarbon nanotubes substantially parallel to each other, and combined byvan der Waals attractive force therebetween. The carbon nanotubesegments can vary in width, thickness, uniformity and shape. Length ofthe untwisted carbon nanotube wire can be arbitrarily set as desired. Adiameter of the untwisted carbon nanotube wire ranges from about 0.5nanometers to about 100 micrometers.

The twisted carbon nanotube wire can be formed by twisting a drawncarbon nanotube film using a mechanical force to turn the two ends ofthe drawn carbon nanotube film in opposite directions. Referring to FIG.7, the twisted carbon nanotube wire includes a plurality of carbonnanotubes helically oriented around an axial direction of the twistedcarbon nanotube wire. More specifically, the twisted carbon nanotubewire includes a plurality of successive carbon nanotube segments joinedend to end by van der Waals attractive force therebetween. Each carbonnanotube segment includes a plurality of carbon nanotubes parallel toeach other, and combined by van der Waals attractive force therebetween.Length of the carbon nanotube wire can be set as desired. A diameter ofthe twisted carbon nanotube wire can be from about 0.5 nm to about 100μm. Further, the twisted carbon nanotube wire can be treated with avolatile organic solvent after being twisted. After being soaked by theorganic solvent, the adjacent paralleled carbon nanotubes in the twistedcarbon nanotube wire will bundle together, due to the surface tension ofthe organic solvent when the organic solvent volatilizing. The specificsurface area of the twisted carbon nanotube wire will decrease, whilethe density and strength of the twisted carbon nanotube wire will beincreased. The deformation of the sound wave generator 110 can beavoided during working, and the distortion degree of the sound wave canbe reduced.

In some embodiments, the sound wave generator 110 is a single drawncarbon nanotube film drawn from the carbon nanotube array. The drawncarbon nanotube film has a thickness of about 50 nanometers, and has atransmittance of visible lights in a range from 67% to 95%.

In other embodiments, the sound wave generator 110 can be or include afree-standing carbon nanotube composite structure. The carbon nanotubecomposite structure can be formed by depositing at least a conductivelayer on the outer surface of the individual carbon nanotubes in theabove-described carbon nanotube structure. The carbon nanotubes can beindividually coated or partially covered with conductive material.Thereby, the carbon nanotube composite structure can inherit theproperties of the carbon nanotube structure such as the large specificsurface area, the high transparency, the small heat capacity per unitarea. Further, the conductivity of the carbon nanotube compositestructure is greater than the pure carbon nanotube structure. Thereby,the driven voltage of the sound wave generator 110 using a coated carbonnanotube composite structure will be decreased. The conductive materialcan be placed on the carbon nanotubes by using a method of vacuumevaporation, spattering, chemical vapor deposition (CVD),electroplating, or electroless plating.

The first electrode 130 and the second electrode 140 are in electricalcontact with the sound wave generator 110, and input electrical signalsinto the sound wave generator 110.

The first electrode 130 and the second electrode 140 are made ofconductive material. The shape of the first electrode 130 or the secondelectrode 140 is not limited and can be lamellar, rod, wire, and blockamong other shapes. A material of the first electrode 130 or the secondelectrode 140 can be metals, conductive adhesives, carbon nanotubes, andindium tin oxides among other conductive materials. The first electrode130 and the second electrode 140 can be metal wire or conductivematerial layers, such as metal layers formed by a sputtering method, orconductive paste layers formed by a method of screen-printing.

The first electrode 130 and the second electrode 140 can be electricallyconnected to two terminals of an electrical signal input device (such asa MP3 player) by a conductive wire. Thereby, electrical signals outputfrom the electrical signal device can be input into the sound wavegenerator 110 through the first electrodes 130, and the secondelectrodes 140.

The plurality of thermoacoustic device units 200 is independent fromeach other. The work status of each thermoacoustic device unit 200 canbe controlled separately and independently by inputting separatesignals.

In one embodiment, a plurality of thermoacoustic device units 200 can belocated on a second surface 103 of the substrate 100. The second surface103 of the substrate 100 is opposite to the first surface 101. Theplurality of thermoacoustic device units 200 on the first surface 101and the second surface 103 are located with a one-to-one correspondence.The plurality of thermoacoustic device units 200 on the first surface101 and the second surface 103 can work together by inputting the samesignals or work individually by inputting different signals. When theplurality of thermoacoustic device units 200 on one surface fail towork, the plurality of thermoacoustic device units 200 on the othersurface will still working. The thermoacoustic device array 10 has along working lifespan.

Furthermore, a heat sink (not shown) can be located on the substrate100, and the heat produced by the sound wave generator 110 can betransferred into the heat sink and the temperature of the sound wavegenerator 110 can be reduced.

The sound wave generator 110 is driven by electrical signals andconverts the electrical signals into heat energy. The heat capacity perunit area of the carbon nanotube structure is extremely small, and thus,the temperature of the carbon nanotube structure can change rapidly.Thermal waves, which are propagated into surrounding medium, areobtained. Therefore, the surrounding medium, such as ambient air, can beheated at a frequency. The thermal waves produce pressure waves in thesurrounding medium, resulting in sound wave generation. In this process,it is the thermal expansion and contraction of the medium in thevicinity of the sound wave generator 110 that produces sound. Theoperating principle of the sound wave generator 110 is the“optical-thermal-sound” conversion.

The thermoacoustic device array 10 has following advantages. First, thewidth of the recess 102 is equal to or greater than 0.2 millimeters andsmaller than or equal to 1 millimeter, thus the carbon nanotubestructure can be effectively protected from being broken. Second, thethermoacoustic device array 10 can be reworked; the plurality of thethermoacoustic device units 200 can be easily divided into individualthermoacoustic device units 200 by cutting the substrate 100 along theplurality of cutting lines 105.

Referring to FIG. 8, one embodiment of a method for makingthermoacoustic device array 10 includes following steps:

(S11) providing a substrate 100 having a first surface 101, wherein thefirst surface 101 defines a grid having a plurality of cells;

(S12) forming a plurality of recesses 102 on each of the plurality ofcells, wherein the plurality of recesses 102 are parallel with andspaced from each other;

(S13) forming a first electrode 130 and a second electrode 140 on eachof the plurality of cells, wherein the first electrode 130 is spacedfrom the second electrode 140, and one of the plurality of recesses 102is located between the first electrode 130 and the second electrode 140;

(S14) applying a sound wave generator 110 on the substrate 100 andelectrically connecting the sound wave generator 110 to the firstelectrode 130 and the second electrode 140, wherein the sound wavegenerator 110 is suspended over the plurality of recesses 102; and

(S15) forming a thermoacoustic device array 10 by separating the soundwave generator 110 according to the plurality of cells, and adjacent twocells are insulated from each other.

In step (S11), the grid can be defined by a plurality of cutting lines105. The plurality of cutting lines 105 can be formed on the substrate100 by etching method. The arrangement of the plurality of cutting lines105 can be selected according to the shape of the thermoacoustic devicearray 10. In one embodiment, the plurality of cutting lines 105 areintersected with each other, and the substrate 100 is divided into aplurality of rectangular cells. The plurality of cutting lines 105 canbe formed via a mechanical or chemical method, such as cutting,grinding, and etching. In one embodiment, as shown in FIG. 15, theplurality of cutting lines 105 is formed by following substeps:

(S111) placing a patterned mask layer 107 on the substrate 100;

(S112) etching the substrate 100 to form the plurality of cutting lines105 through the patterned mask layer 107; and

(S113) removing the mask layer 107.

In step (S111), the mask layer 107 defines a plurality of openings. Thesubstrate 100 is exposed through the plurality of openings. The shape ofthe opening can be circular, square, or rectangular. The material of themask layer 107 can be selected according to the substrate 100, such assilicon dioxide, silicon nitride, silicon oxynitride, or titaniumdioxide. The mask layer 107 can protect one part of the substrate 100which is sheltered by the mask layer 107 from being corrupted by thesolution. In one embodiment, the shape of the opening is rectangular,and a width of the opening ranges from about 0.2 millimeters to about 2millimeter. A length of the opening is selected according to the shapeand the size of the substrate 100. In one embodiment, the width of thesubstrate 100 is 0.15 millimeters and the length of the substrate 100 is8 millimeters.

In step (S112), the substrate 100 can be etched by an etching solution.The etching solution can be an alkaline solution. In one embodiment, theetching solution is potassium hydroxide in a temperature about 80° C.During etching process, the plurality of cutting lines 105 is formed inthe substrate 100.

Furthermore, because the material of the substrate 100 is silicon, thusthe cross section of the cutting line 105 depends on the crystal planeangle silicon. In one embodiment, the cross section of the cutting line105 is in a shape of trapezium.

In step (S113), the mask layer 107 can be removed by dissolved in asolution. In one embodiment, the mask layer 107 is removed byhydrofluoric acid.

In step (S12), the substrate 100 includes a first surface 101 and asecond surface 103 opposite to the first surface 101. The plurality ofrecesses 102 are formed on the first surface 101, and a bulge 104 isformed between the adjacent two recesses 102. The plurality of recesses102 is formed via dry etching or wet etching. In one embodiment, theplurality of recesses 102 is formed via wet etching. As shown in FIG.16, the plurality of recesses 102 is formed by the following substeps:

(S121) placing a patterned mask layer 107 on the first surface 101 ofthe substrate 100;

(S122) etching each cell of the substrate 100 to form the plurality ofrecesses 102, wherein the plurality of recesses 102 are spaced from eachother; and

(S123) removing the mask layer 107.

Steps (S121) to (S123) are the same as steps (S111) to (S113). The masklayer 107 defines a plurality of openings extending along the samedirection, thus the plurality of recesses 102 is extending along thesame direction. Recesses of adjacent two cells are disconnected. Thedepth of the plurality of recesses 102 ranges from about 100 micrometersto about 200 micrometers. The width of each of the plurality of recesses102 ranges from about 0.2 millimeters to about 1 millimeter. Thedistance between adjacent two recesses 102 ranges from about 20micrometers to about 200 micrometers.

Steps (S11) and (S12) can be preformed in one step. The plurality ofcutting lines 105 and the plurality of the recesses 102 can be formed atthe same time. Although the plurality of cutting lines 105 and theplurality of the recesses 102 are formed in the same process, thefunctions of the cutting lines 105 and the recesses 102 are different.The function of the plurality of cutting lines 105 is to define theplurality of cells and separate the plurality of the thermoacousticdevice units 200. The function of the plurality of the recesses 102 isto allow the sound wave generator 110 to be suspended with enoughdistance to produce sound.

In step (S13), the first electrode 130 and the second electrode 140 arelocated apart from each other on two opposite sides of each of theplurality of cells of the substrate 100. In one embodiment, the firstelectrode 130 and the second electrode 140 are deposited on the bulge104. The first electrode 130 and the second electrode 140 can be linearstructure extending parallel with the plurality of bulges 104. In oneembodiment, the first electrode 130 and the second electrode 140 aredeposited on the bulges 104 via imprinting method.

In step (S14), as shown in FIG. 17, the sound wave generator 110 can belocated on the substrate 100 by following substeps:

(S141) providing a carbon nanotube film 108;

(S142) applying the carbon nanotube film 108 on the first surface 101 ofthe subsrate 100, wherein the carbon nanotube film 108 is suspended overthe plurality of recesses 102.

In step (S141), the carbon nanotube film 108 can be a drawn carbonnanotube film 108 drawn from a carbon nanotube array. The drawn carbonnanotube film 108 can be directly attached on the substrate 100. Thedrawn carbon nanotube film 108 includes a plurality of carbon nanotubessubstantially oriented along the same direction. The oriented directionof the plurality of carbon nanotubes is intersected with the extendingdirection of the plurality of recesses 102. In one embodiment, theoriented direction of the plurality of carbon nanotubes is perpendicularto the extending direction of the plurality of recesses 102.

In step (S142), the carbon nanotube film 108 defines a first part and asecond part. In one embodiment, the first part of the carbon nanotubefilm 108 is suspended over the plurality of recesses 102, and the secondpart of the carbon nanotube film 108 is attached on the first electrode130 and the second electrode 140.

Furthermore, a fixed element (now shown) can be located on the soundwave generator 110 to fix the sound wave generator 110. The fixedelement can be attached on the sound wave generator 110 by imprinting orcoating method. In one embodiment, the fixed element is metallic fibersfixed on the sound wave generator 110 and the substrate 100.

In one embodiment, the first electrode 130 and the second electrode 140can be applied after locating the carbon nanotube film 108 on theinsulating layer 120. The first electrode 130 and the second electrode140 is attached on and electrically connected to the carbon nanotubefilm 108. The plurality of carbon nanotubes in the carbon nanotube film108 extends from the first electrode 130 to the second electrode 140.Furthermore, the carbon nanotube film 108 can be firmly fixed on thesubstrate 100 by the first electrode 130 and the second electrode 140.

In step (S15), the method of separating the sound wave generator 110 isselected according to need. In one embodiment, a laser beam separatesthe carbon nanotube film 108. After being separated, the carbon nanotubefilm 108 is further treated. The carbon nanotube film 108 can be treatedby following substeps:

(S151) forming a plurality of carbon nanotube belts 109 by cutting thecarbon nanotube film 108; and

(S152) shrinking the plurality of carbon nanotube belts 109.

In step (S151), the carbon nanotube film 108 can be cut with a laserdevice (not shown). The laser device emits a pulse laser beam. The laserdevice can be an argon ion laser or a carbon dioxide laser. The power ofthe laser device can range from about 1 watt to about 100 watts. In oneembodiment, the laser device can have a power of approximately 12 watts.The laser beam is irradiated on the carbon nanotube film 108, and alaser spot can be formed on the carbon nanotube film 108. The laser spotcan be round in shape and have a diameter ranging from about 1micrometer to about 5 millimeters (e.g. about 20 micrometers). It isnoteworthy that the laser beam can be focused by a lens. It is alsonoteworthy that a number of laser devices can be adopted to adjust theshape of the laser spot. In one embodiment, the laser spot can have astrip shape having a width ranging from about 1 micrometer to about 5millimeters.

The carbon nanotube film 108 and the laser beam are controlled to moverelative to each other so the laser spot moves relative to the carbonnanotube film 108. In one embodiment, the irradiated direction of thelaser beam is substantially perpendicular to the carbon nanotube film108. At the same time, the laser spot moves along a direction whichperpendicular to oriented direction of the carbon nanotubes of thecarbon nanotube film 108. The oriented direction of the carbon nanotubesof the carbon nanotube film 108 is defined as direction X, thus thelaser spot moves substantially parallel with the direction X.

In one embodiment, the carbon nanotube film 108 can be fixed, and thelaser device can be moved to irradiate selected portions of the carbonnanotube film 108 along a scanning path. In another embodiment, thelaser device can be fixed, and the carbon nanotube film 108 can be movedrelative to the laser beam so that the laser beam can irradiate someportions of the carbon nanotube film 108 on the scanning path. In oneembodiment, the carbon nanotube film 108 and the laser device can befixed, and the emergence angle of the laser beam can be adjusted tocause the laser beam moving relative to the carbon nanotube film 108, sothe laser spot can be projected on the selected portions of the carbonnanotube film 108. The laser spot cuts the carbon nanotube film 108 witha certain interval along the oriented direction of the carbon nanotubes.The distance can be substantially the same.

During the process of cutting the carbon nanotube film 108, a pluralityof carbon nanotube belts 109 is formed. The plurality of carbon nanotubebelts 109 are substantially parallel with each other. The plurality ofcarbon nanotube belts 109 can have a substantially uniform width. Thewidth of the carbon nanotube belt can range from about 10 micrometers toabout 50 micrometers to avoid broken or fracture during shrinking thecarbon nanotube belt. Microscopically, some two or more adjacent carbonnanotubes are still joined end to end in each carbon nanotube belt afterthe carbon nanotube film 108 being cut. The carbon nanotubes aresubstantially parallel with each other.

In step (S152), the plurality of carbon nanotube belts 109 can be shrunkby dipping organic solvent. The plurality of carbon nanotube belts 109can also be immersed into the organic solvent. Referring to FIG. 9, theplurality of carbon nanotube belts 109 is shrunk to form the pluralityof carbon nanotube wires 115 (the dark portion is the substrate 100, andthe white portions are the first electrode 130 and the second electrode140). The two opposite ends of the plurality of carbon nanotube wires115 are electrically connected to the first electrode 130 and the secondelectrode 140. The diameter of the carbon nanotube wires 115 ranges fromabout 0.5 micrometers to about 3 micrometers. In one embodiment, thediameter of the carbon nanotube wire is about 1 micrometer, and thedistance between adjacent two carbon nanotube wires 115 is about 120micrometers.

After treating the carbon nanotube film 108, the driven voltage betweenthe first electrode 130 and the second electrode 140 can be reduced.Furthermore, during shrinking process, the organic solvent will notshrink a part of the plurality of carbon nanotube belts 109 attached onthe plurality of bulges 104. Thus after being shrunk, this part of theplurality of carbon nanotube wires 115 can be firmly fixed on the bulges104, and electrically connected to the first electrode 130 and thesecond electrode 140.

The method of making thermoacoustic device array 10 has followingadvantages. Because the first surface 101 of the substrate 100 definesthe plurality of cells and the plurality of thermoacoustic device units200 is formed in the plurality of cells at the same time, thus theproductivity of the plurality of thermoacoustic device units 200 can beincreased.

Referring to FIGS. 10-12, one embodiment of a thermoacoustic devicearray 20 includes a substrate 100 and a plurality of thermoacousticdevice units 300. The substrate 100 includes a first surface 101. Theplurality of thermoacoustic device units 300 is located on the firstsurface 101 of the substrate 100. Each of the plurality ofthermoacoustic device units 300 includes a sound wave generator 110, aplurality of first electrodes 130 and a plurality of second electrodes140. A plurality of recesses 102 is defined by the substrate 100. Theplurality of recesses 102 are spaced from each other and located on thefirst surface 101 of the substrate 100. The sound wave generator 110 isattached on the first surface 101 and is suspended over the plurality ofrecesses 102. Each of the plurality of first electrodes 130 and each ofthe plurality of second electrodes 140 are spaced from each other. Atleast one recess 102 is located between each of the plurality of firstelectrodes 130 and each of the plurality of second electrodes 140. Eachof the plurality of first electrodes 130 and each of the plurality ofsecond electrodes 140 are electrically connected to the sound wavegenerator 110.

The structure of the thermoacoustic device array 20 is similar to thatof the thermoacoustic device array 10, except that the thermoacousticdevice array 20 includes the plurality of first electrodes 130 and theplurality of second electrodes 140.

The plurality of first electrodes 130 and the plurality of secondelectrodes 140 can be arranged as a staggered manner of “a-b-a-b-a-b . .. ”. All the plurality of first electrodes 130 is electrically connectedtogether and all the plurality of second electrodes 140 is electricallyconnected together, whereby the sections of the sound wave generator 110between the adjacent first electrode 130 and the second electrode 140are in parallel. An electrical signal is conducted in the sound wavegenerator 110 from the plurality of first electrodes 130 to theplurality of second electrodes 140. By placing the sections in parallel,the resistance of the thermoacoustic device unit is decreased.Therefore, the driving voltage of the thermoacoustic device unit can bedecreased with the same effect.

The plurality of first electrodes 130 and the plurality of secondelectrodes 140 can be substantially parallel to each other with a samedistance between the adjacent first electrode 130 and the secondelectrode 140. The plurality of first electrodes 130 and the pluralityof second electrodes 140 are alternatively located on the plurality ofbulges 104. The sound wave generator 110 between adjacent firstelectrodes 130 and the second electrodes 140 is suspended over theplurality of recesses 102.

To connect all the plurality of first electrodes 130 together, andconnect all the plurality of second electrodes 140 together, firstconducting member and second conducting member can be arranged. All theplurality of first electrodes 130 are connected to the first conductingmember. All the plurality of second electrodes 140 are connected to thesecond conducting member. The sound wave generator 110 is divided by theplurality of first electrodes 130 and the plurality of second electrodes140 into many sections. The sections of the sound wave generator 110between the adjacent first electrode 130 and the second electrode 140are in parallel. An electrical signal is conducted in the sound wavegenerator 110 from the plurality of first electrodes 130 to theplurality of second electrodes 140.

The first conducting member and the second conducting member can be madeof the same material as the plurality of first electrodes 130 and theplurality of second electrodes 140, and can be perpendicular to theplurality of first electrodes 130 and the plurality of second electrodes140.

Referring to FIG. 13, one embodiment of a thermoacoustic device array 30includes a substrate 100 and a plurality of thermoacoustic device units400. The substrate 100 includes a first surface 101. The plurality ofthermoacoustic device units 400 is located on the first surface 101 ofthe substrate 100. Each of the plurality of thermoacoustic device units400 includes a sound wave generator 110, a plurality of first electrodes130 and a plurality of second electrodes 140. A plurality of holes 106is defined by the substrate 100. The plurality of holes 106 are spacedfrom each other and located on the first surface 101 of the substrate100 uniformly. The sound wave generator 110 is attached on the firstsurface 101 and is suspended over the plurality of holes 106. Each ofthe plurality of first electrodes 130 and each of the plurality ofsecond electrodes 140 are spaced from each other. At least one hole 106is located between each of the plurality of first electrodes 130 andeach of the plurality of second electrodes 140. Each of the plurality offirst electrodes 130 and each of the plurality of second electrodes 140are electrically connected to the sound wave generator 110.

The structure of the thermoacoustic device array 30 is similar to thatof the thermoacoustic device array 20 except that the thermoacousticdevice array 30 includes the plurality of holes 106, and the sound wavegenerator 110 is suspended over the plurality of holes 106.

Each of the plurality of holes 106 has a circular or ellipse opening onthe first surface. The plurality of holes 106 are arranged in an arrayor stagger structure. The depth of each of the plurality of holes 106ranges from about 100 micrometers to about 200 micrometers. The width ofthe opening of each of the plurality of holes 106 ranges from about 0.2millimeters to about 1 millimeter. In one embodiment, the plurality ofholes 106 are arranged in an array, the opening of each of the pluralityof holes 106 is circular, and the diameter of each of the plurality ofholes 106 is about 0.6 millimeters.

Referring to FIG. 14, one embodiment of a thermoacoustic device array 40includes a substrate 100 and a plurality of thermoacoustic device units500. The substrate 100 includes a first surface 101. The plurality ofthermoacoustic device units 500 are located on the first surface 101 ofthe substrate 100. Each of the plurality of thermoacoustic device units500 includes a sound wave generator 110, a plurality of first electrodes130 and a plurality of second electrodes 140. A plurality of recesses102 is defined by the substrate 100. The plurality of recesses 102 arespaced from each other and located on the first surface 101 of thesubstrate 100. The sound wave generator 110 is attached on the firstsurface 101 and is suspended over the plurality of recesses 102. Each ofthe plurality of first electrodes 130 and each of the plurality ofsecond electrodes 140 are spaced from each other. At least one recess102 is located between each of the plurality of first electrodes 130 andeach of the plurality of second electrodes 140. Each of the plurality offirst electrodes 130 and each of the plurality of second electrodes 140are electrically connected to the sound wave generator 110.

The structure of the thermoacoustic device array 40 can be similar tothat of the thermoacoustic device array 20, except that the sound wavegenerator 110 is located between the substrate 100 and the plurality offirst electrodes 130 or the plurality of second electrodes 140. Thesound wave generator 110 is fixed by the plurality of first electrodes130 and the plurality of second electrodes 140.

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may include some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

It is to be understood that the above-described embodiments are intendedto illustrate rather than limit the invention. Variations may be made tothe embodiments without departing from the spirit of the invention asclaimed. Any elements discussed with any embodiment are envisioned to beable to be used with the other embodiments. The above-describedembodiments illustrate the scope of the invention but do not restrictthe scope of the invention.

What is claimed is:
 1. A thermoacoustic device array, the thermoacousticdevice array comprising: a substrate having a surface, wherein thesubstrate defines a plurality of recesses on the surface of thesubstrate, and the plurality of recesses are spaced from and parallelwith each other; a plurality of thermoacoustic device units located onthe surface of the substrate; each of the plurality of thermoacousticdevice units comprising: a sound wave generator located on the surfaceof the substrate and suspended over the plurality of recesses; a firstelectrode and a second electrode spaced from each other and electricallyconnected to the sound wave generator, wherein at least one of theplurality of recesses is located between the first electrode and thesecond electrode, and one portion of the sound wave generator that isbetween the first electrode and the second electrode is suspended overthe at least one of the plurality of recesses.
 2. The thermoacousticdevice array of claim 1, wherein the substrate comprises silicon.
 3. Thethermoacoustic device array of claim 1, wherein the sound wavegenerators of adjacent two thermoacoustic device units are insulatedfrom each other.
 4. The thermoacoustic device array of claim 1, whereinthe substrate further defines a plurality of cutting lines on thesurface, and adjacent two thermoacoustic device units are separated andlocated independently by the plurality of cutting lines.
 5. Thethermoacoustic device array of claim 1, wherein each of the plurality ofthermoacoustic device units further comprises an insulating layerlocated between the surface of the substrate and the sound wavegenerator.
 6. The thermoacoustic device array of claim 1, wherein thesound wave generator is located between the surface of the substrate andthe first electrode or the second electrode.
 7. The thermoacousticdevice array of claim 1, wherein the first electrode or the secondelectrode is located between the surface of the substrate and the soundwave generator.
 8. The thermoacoustic device array of claim 1, whereinthe substrate further comprises a plurality of bulges, and each of theplurality of bulges is located between adjacent two recesses.
 9. Thethermoacoustic device array of claim 8, wherein each of the plurality ofthermoacoustic device units comprises a plurality of third electrodesand a plurality of fourth electrodes, the plurality of third electrodesand the plurality of fourth electrodes are alternatively on theplurality of bulges, the plurality of third electrodes is electricallyconnected, and the plurality of fourth electrodes is electricallyconnected.
 10. The thermoacoustic device array of claim 1, wherein thesound wave generator comprises a carbon nanotube structure, and thecarbon nanotube structure comprises a plurality of carbon nanotubessubstantially oriented along a first direction and parallel with thesurface of the substrate.
 11. The thermoacoustic device array of claim10, wherein the plurality of carbon nanotubes are joined end to endalong the first direction.
 12. The thermoacoustic device array of claim10, wherein the plurality of recesses extends along a second direction,an angel is formed by the first direction and the second direction, andthe angel is greater than 0 degrees and less than or equal to 90degrees.
 13. The thermoacoustic device array of claim 10, wherein thesound wave generator comprises a plurality of carbon nanotube wiresextending along a same direction, and the plurality of carbon nanotubewires are parallel with and spaced from each other.
 14. Thethermoacoustic device array of claim 10, wherein a depth of each of theplurality of recesses ranges from about 100 micrometers to about 200micrometers, and a width of each of the plurality of recesses is greaterthan or equal to 0.2 millimeters and smaller than 1 millimeter.
 15. Athermoacoustic device array, the thermoacoustic device array comprising:a substrate having a surface, wherein the substrate defines a pluralityof holes on the surface of the substrate, and the plurality of holes arespaced from each other and located on the surface uniformly; a pluralityof thermoacoustic device units located on the surface of the substrate;each of the plurality of thermoacoustic device units comprising: a soundwave generator located on the surface of the substrate and suspendedover the plurality of holes; a first electrode and a second electrodespaced from each other and electrically connected to the sound wavegenerator, wherein at least one of the plurality of recesses is locatedbetween the first electrode and the second electrode, and one portion ofthe sound wave generator that is between the first electrode and thesecond electrode is suspended over the at least one of the plurality ofholes.
 16. The thermoacoustic device array of claim 15, wherein theplurality of holes are arranged in an array or stagger structure. 17.The thermoacoustic device array of claim 15, wherein a depth of each ofthe plurality of holes ranges from about 100 micrometers to about 200micrometers.